linux-kernel - Re: [PATCHv6 2/2] watchdog/softlockup: report the most frequent interrupts

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Date: Sun, 11 Feb 2024 23:41:23 +0800
From: Bitao Hu <yaoma@...ux.alibaba.com>
To: Doug Anderson <dianders@...omium.org>
Cc: akpm@...ux-foundation.org, pmladek@...e.com, kernelfans@...il.com,
 liusong@...ux.alibaba.com, linux-kernel@...r.kernel.org,
 yaoma@...ux.alibaba.com
Subject: Re: [PATCHv6 2/2] watchdog/softlockup: report the most frequent
 interrupts



On 2024/2/9 00:03, Doug Anderson wrote:
> Hi,
> 
> On Thu, Feb 8, 2024 at 4:54 AM Bitao Hu <yaoma@...ux.alibaba.com> wrote:
>>
>> +static void start_counting_irqs(void)
>> +{
>> +       int i;
>> +       int local_nr_irqs;
>> +       struct irq_desc *desc;
>> +       u32 *counts = __this_cpu_read(hardirq_counts);
>> +
>> +       if (!counts) {
>> +               /*
>> +                * nr_irqs has the potential to grow at runtime. We should read
>> +                * it and store locally to avoid array out-of-bounds access.
>> +                */
>> +               local_nr_irqs = READ_ONCE(nr_irqs);
> 
> nit: I don't think the READ_ONCE() is actually needed above. All that
> matters is that you're consistently using the same local variable
> ("local_nr_irqs") for allocating the array, looping, and then storing.
> No matter what optimizations might be happening and what else might be
> happening on other CPUs, once you put it in a local variable the
> compiler _must_ keep it consistent.
Oh, yes, READ_ONCE() is not necessary here.
> 
> That being said, I don't think it really matters, so I'm not sure it's
> worth spinning your series just for that.
> 
> In any case, this patch looks good to me now. Thanks!
> 
> Reviewed-by: Douglas Anderson <dianders@...omium.org>